Design View: no undo block may open over the reclaim span, and a reapply closes none

Every opener ends the span first, so a tag fired mid-drain no longer hijacks the
switch's point. One stated criterion governs both lane sites; no-op actions discard.

src/shell/view/view_lanes.h

@@ -15,8 +15,8 @@ class ReaProject;
 namespace reasampler {
 
 // `freeMode` alone decides whether UpdateTimeline is owed (SDK: required after an
-// I_FREEMODE change); `wrote` is any project write at all, which is what the apply's
-// undo-point decision reads.
+// I_FREEMODE change); `wrote` is a REAPER write, the reading ModeApplyResult
+// (view.h) carries through to the caller's undo-point decision.
 struct LaneApplyResult {
     bool freeMode = false;
     bool wrote    = false;
@@ -24,14 +24,22 @@ struct LaneApplyResult {
 
 // Reconciles each op's durable laneKey to the track's current ordinal (a
 // stale/renamed/deleted key is pruned, never mis-driven) and drives C_LANEPLAYS.
+//
+// Opens NO undo block, where mintManagedLanes below opens one over the same
+// parameters — the one criterion this directory's CLAUDE.md states, applied: this
+// re-asserts derived state the view model recomputes from membership on every apply,
+// so nothing here needs to survive as a point of its own; minting creates lanes and
+// re-homes items, which no re-derivation reproduces.
 LaneApplyResult applyLaneOps(const TrackByGuid& handleByGuid,
                              const std::vector<LanePlayOp>& lanes);
 
 // Splits any track visible in more than one mode while carrying its own media into
 // fixed lanes (one managed lane per involved mode), assigns items, and records
-// ownership in `model`. Wraps the mutation in one Undo block when non-empty. Returns
-// true if any lane was minted (repaint hint). `proj` == nullptr means the current
-// project.
+// ownership in `model`. Wraps the mutation in one Undo block when non-empty — see
+// applyLaneOps above for why this site opens one and that one does not — and ENDS THE
+// RECLAIM SPAN first, since REAPER's blocks are a depth counter and this is reachable
+// from a timer tick with a prior switch's span still open. Returns true if any lane
+// was minted (repaint hint). `proj` == nullptr means the current project.
 bool mintManagedLanes(ViewModeModel& model, ReaProject* proj);
 
 // Recovers managed-lane ownership from durable P_LANENAME on project open —